1. Field of the Invention
The present invention relates generally to medical electronic apparatus for applying electrical current to living tissue including programmable apparatus for controlling the electrical current applied therein. More particularly, the present invention relates to a system for controlling the current supplied to an implanted electrode within a body for electrically stimulating a nerve.
2. Description of the Prior Art
Implantable apparatus have been developed in recent years which include an electrode implantable within a living body for electrically stimulating a nerve. Such an apparatus is disclosed in U.S. Pat. No. 3,822,708. In this apparatus, an implantable electrode-carrying device is arranged to be positioned on the spinal cord so that an electric current can be passed through an electrode into a portion of the juxtaposed spinal cord area. The passage of the current into the nerve acts to block electrical pain signals.
More recently, there has been described in U.S. Pat. No. 4,323,073 an apparatus for controlling the direct current applied to living tissue and a method for increasing the current to a predetermined level for a period of time and then decreasing the current. In this manner, no nerve reaction or spasm is caused while the appropriate stimuli is provided for the reduction of pain. This method, however, provides only an automatically modulated output at only one or two levels and does not provide for patient or physician control of the level of stimulation.
Implantable cardiac pacers have utilized programmable devices to establish a desired output in response to transmitted programming signals. Such a device is described in U.S. Pat. No. 4,253,466, where a radio frequency transmitter is used to program an implanted pacemaker. Once programmed, a magnetic field actuated reed relay is used to provide temporary reprogramming and is operable to reset the output to the original setting when the magnetic field is removed.